In some atmospheric conditions, in order to achieve safe, efficient operation, air entering a gas turbine for power generation applications is required to be heated. In one current system, and with reference to FIG. 1 of the drawings, a gas turbine air inlet system 10 includes a main ambient air inlet 12, a filter house 14 and additional inlet ducting at 16, leading to a reduced outlet 18 connected to a gas turbine inlet (not shown). Heating air is introduced via a manifold 20 located in the inlet duct 16, downstream of one or more conventional silencers 22 and upstream of the gas turbine inlet. Hot air is bled from the gas turbine compressor (not shown) and carried via conduit 24 to the manifold 20, controlled by a pressure reducing valve 26.
As best seen in FIG. 1A, the manifold 20 includes a vertical riser 28 connected to the conduit 24, extending upwardly through the manifold. A plurality of horizontally oriented headers 30 (two of several shown) extend in opposite directions from the riser 28, and each includes a plurality of nozzles 32 which introduces the hot compressor-bled air into the duct 16 in a direction opposite the main flow of air entering at the inlet 12. This reverse flow entry of hot air from the compressor promotes good mixing of the hot bleed air with the ambient air flowing into the filter house 14 via inlet 12, towards the manifold 20.
The piping 28, 30 and the manifold 20 are typically stainless steel to prevent scale entering the gas turbine and causing damage. Because the manifold 20 is located near outlet 18 (and hence, the gas turbine inlet), however, mixing is less than ideal. This results in undesirable temperature gradients at the compressor inlet which are magnified at the compressor outlet. The manifold 20 is nevertheless positioned in the inlet duct, downstream of the filter house 14 and the silencer(s) 22 because the manifold is very noisy.
With reference now to FIG. 2, a second known system 34 is similar to the first described system but utilizes compressor bleed air which flows through a conduit 36 under the control of valve 38 and which is introduced through a manifold 40 located upstream of the inlet filter house 42 and adjacent the main inlet 44. The manifold 40 supports an array of silencing nozzles 42 (see FIG. 2A) to maintain an environmentally acceptable sound pressure level.